Chapter 9: Central Nervous System Flashcards
two divisions of the nervous system
1) central nervous system
- brain and spinal cord
- is the integrating centre
2) peripheral nervous system
- all neural tissue outside of the CNS
what are neurons?
neurons are cells that send and receive electrical signals rapidly
role of central nervous system
- consists of the spinal cord and the brain
- integrates information from internal/external environment to illicit appropriate responses for the maintenance of homeostasis
role of peripheral nervous system
- includes all neural tissue outside the CNS
- provides communication between the CNS and the rest of the body
- has two divisions: somatic and autonomic
What is CSF and why is it important?
- cerebrospinal fluid is a clear watery fluid that bathes the brain and spinal cord (the CNS)
- it is important because it helps with protection, nourishment, and waste removal in the brain
main functions of CSF
- CSF cushions the brain (acts as a shock absorber) by preventing the soft nervous tissue from colliding with the hard skull
- CSF helps maintains a stable interstitial fluid environment because it provides neurons and glial cells with essential nutrients and helps with removal of waste products
where does CSF come from?
- it is secreted by the ependymal cells of the ventricles in brain
- CSF is then circulated throughout the four ventricles
how much blood supply is sent to the brain? why so much?
- the CNS receives 15% of the blood that the heart pumps
- a large blood supply is necessary because the CNS tissue has a high rate of metabolic activity compared to most other body tissues
- therefore, it has a high demand for glucose and oxygen to meet its energy needs
what happens if there inadequate blood flow to the brain?
- can result in irreversible damage to CNS tissue
- can cause deficits in certain functions like the ability to speak or move an arm
why is blood flow to the brain critical?
- to help meet the brains energy requirements
- blood flow provides oxygen and glucose to the brain which is needed needs to function properly and stay alive
- neurons in CNS depend on aerobic glycolysis (which requires oxygen and glucose) to maintain ATP levels therefore requiring a steady supply from the blood
what are the different energy supplies to the brain?
- GLUCOSE and oxygen are the main energy supply
- ketones can be used for energy during extreme conditions when glucose supply is limited
why is the CNS so sensitive to changes in blood supply?
it is because the brain and spinal cord have high metabolic demands and limited energy reserves.
- the brain has limited glycogen stores so cells in the CNS must obtain glucose directly from the blood instead
- cells in the CNS do not have access to fatty acids reserves for energy, which increases their demand for glucose
- neurons are more sensitive to oxygen deprivation than other kinds of cells with lower rates of metabolism (because they cannot perform anaeorbic glycolysis)
what are capillaries?
- they are the site of exchange between blood and interstitial fluid
- they’re composed of a thin, single layer of endothelial cells (a type of epithelial cell)
- small wall = short diffusion distance for exchange
what is blood-brain barrier?
- a physical barrier that is selectively permeable
- the capillaries in the brain create protective barrier that restricts the exchange of solutes between blood and brain
how does the blood brain barrier work?
- barrier is the result of tight junctions between capillary endothelial cells
- they eliminate capillary pores which restricts the diffusion of molecules between the cells